1. Field of the Invention
The present invention relates to improvements in rocker arms for internal combustion engines.
2. Description of the Prior Art
The increased demand for internal combustion engines capable of generating higher power while still affording easy maintenance has provided incentive to use advanced materials in the valve train of such engines. One of the efforts in improving the valve train is to employ new materials such as ceramics to make the valve train lighter in weight and more durable. In overhead cam configurations where the cam slides on a portion of the rocker arm, die cast aluminum rocker arms are used with a sintered metal alloy portion cast in place at the location interfacing with the cam. In such a manner, the rocker arm is wear resistant, highly rigid, lightweight and of sufficient strength. In addition, ceramic inserts are increasingly being used in such rocker arms to improve their wear resistant properties during high speed operation because conventional metal inserts used in diesel and LPG engines wear rapidly in such applications.
There have also been attempts to form rocker arms from ceramic materials by monolithic molding to provide a lightweight rigid and wear resistant rocker arm. See, Japanese Application No. 47188/86 by the present applicant.
When such a rocker arm is provided with an adjustment screw or lash adjustment for providing the appropriate valve clearance, it is necessary to bore a hole through the adjustment end of the rocker arm and form internal threads therein. When such a rocker arm is formed of a ceramic, the threads formed prior to sintering are distorted by dimensional changes occurring during the sintering process. In addition, if the threads are mechanically formed after sintering, the processes for forming such threads are relatively difficult because of the high hardness of the sintered ceramic.
Therefore, it is one object of the present invention to provide a valve adjustment mechanism on a ceramic rocker arm that can be inexpensively manufactured.
It is another object of the invention to provide a valve adjustment mechanism for a ceramic rocker arm which can be readily interfaced to the ceramic portion of the rocker arm without expensive forming techniques.
Additional objects and advantages of the invention will be set forth in the description which follows and in part will be obvious from the description or may be learned by practice of the invention. The object and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.